Process of refining hard tin



Patented July 3, 1934 UNITED STATES 1,964,948 PROCESS OF REFINING HARDTIN Walter R. Hibbard and Ellsworth T. Candee,

Waterbury, Conn., assignors to The American Brass Company, tion ofConnecticut No Drawing.

7 Claims.

This invention relates to certain new improvements in the electrolyticrefining of hard tin, or impure tin cast in anodes, and has for anobject to provide an improved process and electrolyte for refining hardtin to a purity satisfactory for use in casting, and also by which thetin is deposited as a dense adherent plate which can be handled or used'in commercial practice, and which is satisfactory for electro-tinning ofcopper sheets, etc.

In the practice of the invention the electrolyte solution ispreferably-prepared by dissolving the required amount of sulphuric acidin water, adding the pyroligneous acid and flake glue previouslydissolved in water and electrolyzing, using the impure tin as anodes. Inthis way the solution is built up by electrolysis but we are notnecessarily confined to this method of preparing the solution. In thelaboratory. the electrolyte was also prepared by dissolving pure tin inboiling 1-1 sulphuric acid and then diluting with water -to the correctvolume. The pyroligneous acid and glue were added as above. This methodof making up the electrolyte solution was used in the laboratory so asto avoid wating two weeksfor it to build up by electrolysis.

The addition agent is preferably prepared by taking crude pyroligneousacid and subjecting it to fractional distillation and we use all theresidue that does not come oil at approximately 100.5 degrees C. Thatis, we use the fraction that is left after bringing it up to 1(l0.5 C.and therefore discard all that boils below 100.5 C. The residueremaining in the still is from 10 to 15% of the volume of thepyroligneous acid distilled.

This liquid is a very dark brown liquid (density approximately 1.066)having the odor of burnt wood and is soluble in water and dilute acids.Although we prefer to use this residue in preparing the electrolyte weare not necessarily limited thereto as we may use the pyroligneous acidwithout distilling, but the elements of this acid which distill offbelow 100.5 C. do not appear to have any beneficial effect. 7Pyroligneous acid is the liquid which is collected from the distillationof hard wood after the tarry material has been removed. It is defined inBernthsen Sudboroughs text book of Organic Chemistry on page 156,edition of 1926 as follows: An aqueous solution known as pyroligneousacid, which, in addition to acetic acid, contains methyl alcohol,acetone, homologues of acetic acid, and strongly smelling combustibleproducts (empyreuma) It was found that the addition of the residueWaterbury, Conn., a corpora- Application November 23, 1932, Serial No.644,076

from the pyroligneous acid alone to the electrolyte would produce asatisfactory plate for certain purposes, and it was also found that theaddition of a colloid such as glue produced a more dense plate andpermitted a higher current density to be used.

In preparing the electrolyte the relative pro-- portions of the variouselements may vary. The electrolyte solution of tin in a free acid ispreferably in the proportions of approximately 2% by weight of the tin,9;'75% by weight of free acid, such for example as sulphuric acid,approximately 0.6% by weight of the pyroligneous acid residue but it mayvary from about 0.1% to about 1.5%, or approximately 5% by weight ofpyroligneous acid if we use it without distilling, and the remainderwater. When glue is added it is preferably used in the proportion ofapproximately 0.001% by weight.

However, the tin may vary from about 0.1% to about 3.5%, the acidcontent from about 6% to about 15% and the amount of addition agent usedmay vary from approximately 1 to 10% by weight of the acid. The glueneeds to be only from about .001% to about 25% by weight of theelectrolyte solution.

The tin produced with this improved electrolyte solution has a highdegree of purity, density and adherent quality. A test showed thefollowing composition:

Percent Copper 0.018 Lead 0.00 Iron 0.018 Tin (Diff) 99.964

This was purified from hard tin having the following composiiton:

Percent Copper 3.95 v5 Lead 1.91 Tin (Difi) 94.14

The purity of the refined tin, however, is not dependent on the presenceof the addition agent as 10% sulphuric acid solution will produce tin ofthe same purity. This while it may be satisfactory as merely a refiningbath does not produce a plate which is satisfactory for electro-tinningof copper sheets and the like, as it does. not have the desired densityand adherent qualities. The chief purpose of the addition agent is toproduce a dense, adherent plate which can be handled in commercialpractice ,and while it was found that the addition of the pyroligneousacid or its residue alone would produce a satisfactory plate for certainpurposes, it was also found that the addition of a colloid such as glueproduced a more dense plate and permitted a higher current density to beused.

A solution which was satisfactory had approximately the followingcomposition:

In 1 gallon In 1 liter of solution of solution Ounccs Grams H1504 13.4100 Stnnnnus tin 2.0-2.7 l5-20 Pyroligncous acid res ue... .8 6 Glue l.75

This solution has been run at a current density of 6 to 10 amperes persquare foot'without any signs of treeing or a non-adherent plate.

Having thus set forth the nature of our invention, what we claim is:

1. A process for the electrolytic refining of impure tin which comprisespassing an electric current from the tin anode to a cathode through anelectrolyte solution approximately 2% by weight of tin, 9.75% by weightof sulphuric acid, and 0.6% by weight of pyroligneous acid residueremaining after distilling pyroligneous acid at approximately 100.5 C.

2. A process for the electroyltic refining of impure tin which comprisespassing an electric current from the tin anode to a cathode through anelectrolyte solution of approximately 2% i by weight of tin in sulphuricacid, and containing from approximately 1% to 10% by weight ofpyroligneous acid residue remaining after distilling pyroligneous acidat approximately l00.5 C.

and a colloid such as glue from about 0.001% to 0.25%.

3. A process for the electrolytic refining of impure tin which comprisespassing an electric current from the tin anode to a cathode through anelectrolyte solutionof approximately 2% by weight of tin, 9.75% byweight of sulphuric acid, 0.6% by weight of pyroligneous acid residueremaining after distilling pyroligneous acid at 100.5 C., glue from0.001% to 0.25% and balance water.

4. An electrolyte for the refining of impure tin comprising anelectrolyte solution of tin in sulphuric acid in the proportions ofapproximately 2% by weight of tin, 9.75% by weight of the acid togetherwith an addition agent containing pyroligneous acid residue remainingafter distilling pyroligneous acid at approximately 100.5 C.

5. An electrolyte for the refining of impure tin comprising anelectrolyte solution of tin in sulphuric acid together with an additionagent containing pyroligneous acid residue remaining after distillingpyroligneous acid at approximately 100.5 C. and a colloid such as glue.

6. An electrolyte for the refining of impure tin comprising anelectrolyte solution of tin in sulphuric acid, pyroligneous acid residueremaining after distilling pyroligneous acid at approximately 100.5 C.from about 1% to about 10%, and glue from 001% to 25%.

'7. An electrolyte for the refining of impure tin comprising anelectrolytic solution of tin in sulphuric acid together with an additionagent containing pyroligneous acid residue remaining after distillingpyroligneous acid at approximately l00.5 C.

WALTER R. HIBBARD. ELLSWORTH T. CANDEE.

